(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2009/0027068 A1
`Philipp et al.
`(43) Pub. Date:
`Jan. 29, 2009
`
`US 20090027O68A1
`
`(54) PROXIMITY SENSOR
`
`(75) Inventors:
`
`Harald Philipp, Southampton
`(GB); Kevin Snoad, Chicester (GB)
`
`Correspondence Address:
`DAVID KEWT
`5901 THIRD ST SOUTH
`ST PETERSBURG, FL 33705 (US)
`
`(73) Assignee:
`
`QRG LIMITED, Eastleigh (GB)
`
`(21) Appl. No.:
`
`12/179,769
`
`(22) Filed:
`
`Jul. 25, 2008
`
`Related U.S. Application Data
`(60) Provisional application No. 60/952,053, filed on Jul.
`26, 2007.
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`GOIR 27/26
`(52) U.S. Cl. ........................................................ 324/678
`(57)
`ABSTRACT
`A capacitive touch sensor providing an automatic Switch-off
`function for an apparatus in which the sensor is incorporated
`is provided. The sensor comprises a sensing element coupled
`to a capacitance measurement circuit for measuring the
`capacitance of the sensing element. A control circuit is oper
`able to determine from the capacitance measurement whether
`an object is in proximity with the sensor. The determined
`presence of an object may be used to toggle a function of the
`apparatus. Furthermore, when it is determined that an object
`has not been in proximity with the sensor for a predetermined
`time duration, an output signal for Switching off the apparatus
`is provided. The predetermined time duration may be selected
`from a number of predefined time durations, or may be pro
`grammed using an resistor-capacitor network. Pulses may be
`applied to the control circuit to override features of the auto
`matic switch-off functionality.
`
`SENSE
`ELECTRODE
`
`
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 1 of 21
`
`

`

`Patent Application Publication
`
`Jan. 29, 2009 Sheet 1 of 10
`
`US 2009/0027068 A1
`
`SENSE
`EECTROE
`
`
`
`VOD
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 2 of 21
`
`

`

`Patent Application Publication
`
`Jan. 29, 2009 Sheet 2 of 10
`
`US 2009/0027068 A1
`
`(Output in On condition)
`h
`
`SNSK
`QT102
`
`->
`
`-- ~2.6ms
`
`Fig. 4
`w
`
`cr5mso
`
`>8
`35
`V
`
`fast detect
`integrator
`
`Sih has health bhhhhh ."
`
`OUT —
`
`
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 3 of 21
`
`

`

`Patent Application Publication
`
`Jan. 29, 2009 Sheet 3 of 10
`
`US 2009/0027068 A1
`
`
`
`
`
`VOD
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 4 of 21
`
`

`

`Patent Application Publication
`
`Jan. 29, 2009 Sheet 4 of 10
`
`US 2009/0027068 A1
`
`
`
`
`
`VDD
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 5 of 21
`
`

`

`Patent Application Publication
`
`Jan. 29, 2009 Sheet 5 of 10
`
`US 2009/0027068 A1
`
`Rm
`
`Fig. 11
`
`VDD
`
`VSS H
`Tp
`
`p
`
`p
`
`p
`
`s
`:
`
`:
`
`Out
`
`
`
`C
`C
`C
`C
`P - override (reload auto off delay)
`O - Switch output off (toff burst time + 50ms)
`C - Sensor recalibration
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 6 of 21
`
`

`

`Patent Application Publication
`
`Jan. 29, 2009 Sheet 6 of 10
`
`US 2009/0027068 A1
`
`QT 102 Active High Output
`
`53
`
`4-He
`45
`-
`RC 43 H-2 H
`Divisor ,
`e-H
`(*)
`37
`2
`35H2--
`33H-H
`21-2H
`-
`29
`2
`2.5
`3
`3.5
`4 4.5
`5
`VDD(volts)
`Fig. 13
`
`QT102 Active Low Output
`
`
`
`RC
`Divisor
`(K)
`
`2
`
`2.5
`
`4
`3.5
`3
`VDD(volts)
`
`4.5
`
`5
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 7 of 21
`
`

`

`Patent Application Publication
`
`Jan. 29, 2009 Sheet 7 of 10
`
`US 2009/0027068 A1
`
`Vm = Vss (delay multiplier = x1)
`
`QT102 Active High Output VDD = 5V
`
`4000
`
`an
`2.
`k 3000
`É 200 || 4 -41.
`
`O
`S 1000
`<g
`
`QT102 Active High Output VDD = 4V
`Cloon?
`Ct-47nf:
`
`- - a
`
`- -
`
`20
`Timing Resistor Rt (Kohms)
`
`to
`
`210
`170
`130
`90
`50
`Timing Resistor Rt (Kohms)
`
`Z
`
`|
`
`-
`
`>
`
`N1
`
`1.
`& 3000
`d
`A 200C
`5
`s to
`
`QT102 Active High Output VDD = 2V
`QT102 Active High Output VDD = 3V
`4000
`Ct. 10On
`4000
`C= 00If
`M
`C-47s 2 2 H PP
`i 3000 HA-1
`2
`2000
`5 277
`O E 1000
`3.
`
`-1 -
`
`
`
`90
`130
`170
`210
`Timing Resistor Rt (Kohms)
`
`O
`
`50
`90
`130
`170
`210
`Timing Resistor Rt (Kohms)
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 8 of 21
`
`

`

`Patent Application Publication
`
`Jan. 29, 2009 Sheet 8 of 10
`
`US 2009/0027068 A1
`
`Vm = Vss (delay multiplier = x1)
`
`QT102 Active Low Output VDD = 5V
`oomf
`
`QT102 Active Low Output VDD = 4V
`4000r-r
`
`
`
`20 00
`
`||
`II/ Y -1 ||
`10ool Y-41 || ||
`4411 || || ||
`0.21 |
`|
`|
`|
`|
`|
`|
`|
`O
`40
`80
`120
`160
`200
`Timing Resistor Rt (Kohms)
`
`2O 00
`
`1000
`e
`|
`|
`|
`|
`|
`|
`|
`o21 ||
`200
`160
`120
`80
`O
`40
`Timing Resistor Rt (Kohms)
`
`QT102 Active Low Output VDD = 3V
`4000
`o
`5. "I
`2 3000
`a 2000
`5" (A -
`S 1000
`3. "A12
`0
`O
`
`QT102 Active Low Output VDD = 2V
`4000
`"Cinf-di-32hf
`o
`i
`2 3000
`r
`2000
`P
`t1.
`O
`S 1000 A4249-21
`3. "A24-21
`21 |
`|
`|
`|
`| |
`|
`O
`40
`80
`120
`160
`200
`Timing Resistor Rt (Kohms)
`
`
`
`160 200
`120
`80
`40
`Timing Resistor Rt (Kohms)
`
`Fig. 16
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 9 of 21
`
`

`

`Patent Application Publication
`
`Jan. 29, 2009 Sheet 9 of 10
`
`US 2009/0027068 A1
`
`SENSE
`ELECTRODE
`
`
`
`SENSE
`ELECTRODE
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 10 of 21
`
`

`

`Patent Application Publication
`
`Jan. 29, 2009 Sheet 10 of 10
`
`US 2009/0027068 A1
`
`
`
`Fig. 20
`
`out.
`
`VSS
`
`SNSK
`
`TIME
`
`VOD
`
`SNS
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 11 of 21
`
`

`

`US 2009/0027068 A1
`
`Jan. 29, 2009
`
`PROXMITY SENSOR
`
`BACKGROUND ART
`
`0001. This invention relates to proximity sensors. In par
`ticular, the invention relates to capacitive sensors for sensing
`the presence or touch of an object adjacent to a sensor.
`0002 Capacitive position sensors have recently become
`increasingly common and accepted in human interfaces and
`for machine control. For example, in the fields of portable
`media players it is now quite common to find capacitive touch
`controls operable through glass or plastic panels. Some
`mobile (cellular) telephones are also starting to implement
`these kinds of interfaces.
`0003. Many capacitive touch controls incorporated into
`consumer electronic devices for appliances provide audio
`and/or visual feedback to a user indicating whetherafinger or
`other pointing object is present or approaches such touch
`controls. A capacitive sensing microprocessor may typically
`be comprised in touch-controlled devices which are arranged
`to provide an “on” output signal when a finger is adjacent to
`a sensor and an “off” output signal when a finger is not
`adjacent to a sensor. The signals are sent to a device controller
`to implement a required function dependent on whether a
`user's finger is in proximity with or touching an associated
`touch control.
`0004 Some touch-controlled devices remain “on” or
`“active' despite the user having moved away from the device
`or a particular function no longer being required. This results
`in the device consuming a large amount of power which is not
`efficient.
`0005. There is therefore a need for an improved capacitive
`touch sensor which can regulate power usage.
`
`SUMMARY OF THE INVENTION
`
`0006. According to a first aspect of the invention there is
`provided a sensor for determining the presence of an object
`comprising: a sensing element; a capacitance measurement
`circuit operable to measure the capacitance of the sensing
`element; and a control circuit operable to determine whether
`an object is in proximity with the sensor based on a measure
`ment of the capacitance of the sensing element, the control
`circuit further being operable to provide an output signal to
`control a function of an apparatus when it is determined that
`an object has not been in proximity with the sensor for a
`predetermined time duration.
`0007. The control circuit may be configured so that the
`predetermined time duration is selectable from a number of
`different predefined time durations.
`0008. The control circuit may include a time input termi
`nal and the predetermined time duration may selectable from
`the number of different predefined time durations according
`to a Voltage applied to the time input terminal.
`0009. The control circuit may include a delay multiplier
`terminal and be configured so that a selected one of the
`number of different predefined time durations is multiplied
`by a multiplication factor according to a Voltage applied to the
`delay multiplier terminal so as to provide the predetermined
`time duration.
`0010. The control circuit may be configured so that the
`predetermined time duration is programmable by a user to
`provide a user-selected time duration.
`
`0011. The sensor may comprise a resistor-capacitor (RC)
`network coupled to the control circuit and the predetermined
`time duration may depend on a time constant of the RC
`network.
`0012. The control circuit may include a delay multiplier
`terminal and be configured so that the user-selected time
`duration is multiplied by a multiplication factor according to
`a Voltage applied to the delay multiplier terminal to provide
`the predetermined time duration.
`0013 The control circuit may be configured such that the
`provision of the output signal to control a function of an
`apparatus after the predetermined time duration may be over
`ridden so the output signal is not provided when it is deter
`mined that an object has not been in proximity with the sensor
`for a predetermined time duration. For example, the control
`circuit may be operable to receive an override pulse and on
`receipt of the override pulse to retrigger the predetermined
`time duration to so as to extend the time before the output
`signal to control a function of an apparatus is provided.
`0014. The control circuit may be configured such that the
`provision of the output signal to control a function of an
`apparatus after the predetermined time duration may be over
`ridden so the output signal is provided before it is determined
`that an object has not been in proximity with the sensor for a
`predetermined time duration. For example, the control circuit
`may be operable to receive an override pulse and on receipt of
`the override pulse to provide the output signal to control a
`function of an apparatus.
`0015 The sensor may be configured to perform a recali
`bration when the sensor is powered up, when an object is
`determined to be in proximity with the sensor for more thana
`timer setting, and/or when an override is released.
`0016. The control circuit may be configured such that the
`output signal is toggled between a high state and a low state
`when an object is determined to be in proximity with the
`SSO.
`0017. The function of an apparatus controlled by the out
`put signal may be a Switch-off function.
`0018. The capacitance measurement circuit may employ
`bursts of charge-transfer cycles to acquire measurements.
`0019. The capacitance measurement circuit may be con
`figured to operate in one of more than one acquisition modes
`depending on the output signal, for example a low-power
`mode or a fast mode.
`0020. The capacitance measurement circuit and the con
`trol circuit may be comprised in a general purpose microcon
`troller under firmware control.
`0021. The capacitance measurement circuit and the con
`trol circuit may be comprised within a six-pin integrated
`circuit chip package, such as an SOT23-6.
`0022. According to a second aspect of the invention there
`is provided apparatus comprising a sensor according to the
`first aspect of the invention.
`0023. According to a third aspect of the invention there is
`provided a method for controlling a function of an apparatus
`comprising: determining whether an object is in proximity
`with a sensor based on a measurement of the capacitance of a
`sensing element and providing an output signal to control the
`function of the apparatus when it is determined that an object
`has not been in proximity with the sensor for a predetermined
`time duration.
`0024. The function of the apparatus controlled by the out
`put signal may be a Switch-off function.
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 12 of 21
`
`

`

`US 2009/0027068 A1
`
`Jan. 29, 2009
`
`0025. According to another aspect of the present inven
`tion, there is provided a sensor for determining the presence
`of an object comprising: a sensing element, a capacitance
`measurement circuit operable to measure the capacitance of
`the sensing element, and a control circuit operable to deter
`mine whether an object is in proximity with the sensor based
`on a measurement of the capacitance of the sensing element,
`the control circuit also being operable to provide an output
`signal to control a function of an apparatus based on an object
`not being in proximity with the sensor and the output signal
`being produced after a predetermined time duration.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`0026. For a better understanding of the invention and to
`show how the same may be carried into effect reference is
`now made by way of example to the accompanying drawings
`in which:
`0027 FIG. 1 schematically shows sense electrode connec
`tions for an example chip for implementing an auto-off func
`tion according to an embodiment of the invention;
`0028 FIG. 2 schematically represent an application of
`drift compensation in the chip of FIG. 1;
`0029 FIG. 3 schematically shows a basic circuit configu
`ration for providing a 15 minute auto Switch-off function in an
`active high output implementation of an embodiment of the
`invention;
`0030 FIG. 4 schematically shows a series of fast mode
`bursts on the SNSK pin of the chip shown in FIG. 1 when in
`an on condition;
`0031
`FIG. 5 schematically shows a series of low-power
`mode bursts and a switch to fast mode power bursts on the
`SNSK pin of the chip shown in FIG. 1 when switching from
`an off condition to an on condition;
`0032 FIG. 6 schematically shows use of an output con
`figuration resistor Rop to configure the chip of FIG. 1 to have
`an active high or an active low output;
`0033 FIG. 7 schematically shows an example circuit con
`figuration for the chip shown in FIG. 1 with the output con
`nected to a digital transistor;
`0034 FIG. 8 schematically shows an example circuit con
`figuration for the chip shown in FIG. 1 configured to provide
`a predefined auto-off delay;
`0035 FIG.9 schematically shows an example circuit con
`figuration for the chip shown in FIG. 1 configured to provide
`a programmable auto-off delay;
`0036 FIG. 10 schematically shows an example pulse
`applied to the chip shown in FIG. 1 to override an auto-off
`delay;
`0037 FIG. 11 schematically shows another example pulse
`applied to the chip shown in FIG. 1 to override an auto-off
`delay;
`0038 FIG. 12 schematically shows example voltage levels
`for the chip shown in FIG. 1 in overriding of an auto-off delay:
`0039 FIGS. 13 and 14 schematically show typical values
`of RC divisor Kas a function of supply voltage VDD for the
`chip shown in FIG. 1 with active high output and active low
`output respectively;
`0040 FIG. 15 schematically shows typical curves of auto
`off delay as a function of timing resistor value for different
`capacitor values and different Supply Voltages for an active
`high output configuration;
`
`0041 FIG.16 schematically shows typical curves of auto
`off delay as a function of timing resistor value for different
`capacitor values and different Supply Voltages for an active
`low output configuration;
`0042 FIG. 17 schematically shows an example applica
`tion of the chip shown in FIG. 1 in an active low output
`configuration driving a PNP transistor with an auto-off time
`of 3.33 hours;
`0043 FIG. 18 schematically shows another example
`application of the chip shown in FIG. 1 in an active high
`output configuration driving a high impedance with an auto
`off time of 135 seconds;
`0044 FIG. 19 schematically shows an implementation of
`the chip shown in FIG. 1 in an SOT23-6 package; and
`0045 FIG. 20 schematically shows a pin diagram for an
`implementation of the chip shown in FIG. 1 in an SOT23-6
`package.
`
`DETAILED DESCRIPTION
`0046. In one example, an embodiment of the invention
`may be implemented in an integrated circuit chip providing a
`proximity sensor function. The integrated circuit chip may
`thus be incorporated into a device or apparatus to provide and
`control a proximity sensor functionality for the device/appa
`ratus in accordance with an embodiment of the invention. For
`the purposes of explanation, a specific integrated circuit chip
`providing the functionality of an embodiment of the invention
`will be described further below. The chip will in places be
`referred to by product name QT102. However, it will be
`appreciated that the QT 102 chip is merely a specific example
`application of an embodiment of the invention. Other
`embodiments of the invention need not be implemented in a
`chip in this way, and furthermore, other embodiments of the
`invention may be provided in conjunction with all. Some or
`none of the additional features of the QT 102 chip described
`further below.
`0047. Before turning specifically to the QT 102 chip
`embodiment, a Summary is provided.
`0048. It is known that a touch sensitive sensor may com
`prise a sensor element, such as an etched copper electrode
`mounted on a PCB substrate, and a control circuit for mea
`Suring a capacitance of the sensor element to a system refer
`ence potential. The sensor element may be referred to as a
`sense electrode. The capacitance of the sense electrode is
`affected by the presence of nearby objects, such as a pointing
`finger. Thus the measured capacitance of the sense electrode,
`and in particular changes in the measured capacitance, may
`be used to identify the presence of an object adjacent the sense
`electrode. The control circuit may be configured to provide an
`output signal, e.g. by setting an output logic level as high or
`low, indicating whether or not an object is deemed to be
`adjacent the sense electrode. A controller of a device in which
`the touch sensitive sensor is implemented may receive the
`output signal and act accordingly.
`0049. There are various known technologies for measur
`ing capacitance of a sense electrode in a capacitive touch
`sensor. Embodiments of the present invention may be imple
`mented in conjunction with any of these technologies/mea
`Surement circuits. For example, the fundamental principles
`underlying the capacitive sensors described in U.S. Pat. No.
`5,730,165, U.S. Pat. No. 6,466,036 and U.S. Pat. No. 6,452,
`514 could be used.
`0050. In accordance with embodiments of the invention,
`the control circuit of the sensor can determine whether an
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 13 of 21
`
`

`

`US 2009/0027068 A1
`
`Jan. 29, 2009
`
`object or a user's finger is no longer in proximity with the
`sensor and based on a pre-determined time duration, the
`control circuit can produce an output signal automatically to
`prevent the capacitance measurement circuit from continu
`ally measuring changes in capacitance due to, for example,
`the perceived presence of an object in proximity with the
`SSO.
`0051. Therefore, the control circuit is able to deactivate,
`turn-off, or power down the capacitance measurement circuit
`where an apparatus has inadvertently been left on or with the
`erroneous perception that a user is still present. This may, for
`example, be referred to as an “auto-off feature. The signal for
`preventing the capacitance measurement circuit from con
`tinually measuring changes in capacitance may be referred to
`as an auto-off signal. The capacitance measurement circuit
`and the auto-off control circuit may be comprised in a gen
`eral-purpose microcontroller under firmware control, for
`example, such as the QT102 chip described further below.
`0052. As described in Section 3.5 of the below numbered
`sections, and in conjunction with the drawings, the control
`circuit of the sensor may be implemented by different meth
`ods—for example, the auto-off signal output may be pro
`duced automatically after different pre-determined time dura
`tions to effect powering down the capacitance measurement
`circuit due to no presence of the user, the control circuit may
`be programmed by a user so that it may power down an
`apparatus based on a user-selected time duration; the control
`circuit output signals may be overridden, for example, to
`extend time durations before an apparatus is turned-off or to
`immediately turn-off an apparatus when a user is no longer
`present.
`0053. The sensor of the invention may be useful in various
`applications, for example in kitchen appliances, light
`Switches, headsets, and other electronic consumer devices.
`For example, a coffee machine incorporating a sensor of the
`invention may be programmed to power-down after a time
`period of, say, 30 minutes, where the coffee machine has been
`left on inadvertently. This will beneficially conserve energy
`use and minimise the possibility of damage and/or accidents
`caused by the coffee machine or glass container(s) overheat
`1ng.
`0054 Aspects of the QT102 chip referred to above, and
`which incorporates an embodiment of the invention, will now
`be described in the following numbered sections.
`0055. The numbered sections may be considered to relate
`generally to features of the QT 102 chip as follows: Section
`1—Overview (including 1.1 Introduction, 1.2 Electrode
`Drive, 1.3 Sensitivity, 1.3.1 Introduction, 1.3.2 Increasing
`Sensitivity, 1.3.3 Decreasing Sensitivity, 1.4 Recalibration
`Timeout, 1.5 Forced Sensor Recalibration, 1.6 Drift Compen
`sation, 1.7 Response Time, 1.8 Spread Spectrum). Section
`2—Wiring and Parts (including 2.1 Application Note, 2.2 Cs
`Sample Capacitor, 2.3 Rs Resistor, 2.4 Power Supply, PCB
`Layout, 2.5 Wiring). Section 3 Operation (including 3.1
`Acquisition Modes, 3.1.1 Introduction, 3.1.2 OUT Pin On
`(Fast Mode), 3.1.3 OUT Pin Off (Low Power Mode), 3.2
`Signal Processing, 3.2.1 Detect Integrator, 3.2.2 Detect
`Threshold, 3.3 Output Polarity Selection, 3.4 Output Drive,
`3.5 Auto Off Delay, 3.5.1 Introduction, 3.5.2 Auto Off
`Predefined Delay, 3.5.3 Auto Off User-programmed Delay,
`3.5.4 Auto Off Overriding the Auto Off Delay, 3.5.5 Con
`figuring the User-programmed Auto-off Delay, 3.6 Examples
`of Typical Applications). Section 4-Specifications (includ
`ing 4.1 Absolute Maximum Specifications, 4.2 Recom
`
`mended Operating Conditions, 4.3 AC Specifications, 4.4
`Signal Processing, 4.5 DC Specifications, 4.6 Mechanical
`Dimensions, 4.7 Moisture Sensitivity Level (MSL)).
`
`1 Overview
`1.1 Introduction
`0056. The QT 102 is a single key device featuring a touch
`on/touch off (toggle) output with a programmable auto
`switch-off capability.
`0057 The QT 102 is a digital burst mode charge-transfer
`(QT) sensor designed specifically for touch controls; it
`includes hardware and signal processing functions to provide
`stable sensing under a wide variety of changing conditions. In
`examples, low cost, non-critical components are employed
`for configuring operation.
`0058. The QT 102 employs bursts of charge-transfer
`cycles to acquire its signal. Burst mode permits power con
`Sumption in the microampere range, dramatically reduces
`radio frequency (RF) emissions, lowers susceptibility to elec
`tromagnetic interference (EMI), and yet permits good
`response time. Internally the signals are digitally processed to
`reject impulse noise, using a consensus filter which in this
`example requires four consecutive confirmations of a detec
`tion before the output is activated.
`0059. The QT switches and charge measurement hard
`ware functions are all internal to the QT 102.
`1.2 Electrode Drive
`0060 FIG. 1 schematically shows the sense electrode con
`nections (SNS, SNSK) for the QT102.
`0061
`For improved noise immunity, it may be helpful if
`the electrode is only connected to the SNSK pin.
`0062. In examples the sample capacitor Cs may be much
`larger than the load capacitance (CX). E.g. typical values for
`Cx are 5 to 20 pF while Cs is usually 1 or 2 to 50 nF. (Note: Cx
`is not a physical discrete component on the PCB, it is the
`capacitance of the touch electrode and wiring. It is shown in
`FIG. 1 to aid understanding of the equivalent circuit.)
`0063 Increasing amounts of Cx destroy gain, therefore it
`is important to limit the amount of load capacitance on both
`SNS terminals. This can be done, for example, by minimizing
`trace lengths and widths and keeping these traces away from
`power or ground traces or copper pours.
`0064. The traces and any components associated with
`SNS and SNSK will become touch sensitive and so may need
`to be considered to help in limiting the touch-sensitive area to
`the desired location.
`0065. A series resistor, Rs, may be placed in line with
`SNSK to the electrode to suppress electrostatic discharge
`(ESD) and Electromagnetic Compatibility (EMC) effects.
`1.3 Sensitivity
`1.3.1 Introduction
`0066. The sensitivity of the QT 102 is a function of such
`things as:
`0067 the value of Cs
`0068 electrode size and capacitance
`0069 electrode shape and orientation
`0070 the composition and aspect of the object to be
`sensed
`0071 the thickness and composition of any overlaying
`panel material
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 14 of 21
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`US 2009/0027068 A1
`
`Jan. 29, 2009
`
`the degree of ground coupling of both sensor and
`
`0072
`object
`1.3.2 Increasing Sensitivity
`0073. In some cases it may be desirable to increase sensi
`tivity; for example, when using the sensor with very thick
`panels having a low dielectric constant. Sensitivity can often
`be increased by using a larger electrode or reducing panel
`thickness. Increasing electrode size can have diminishing
`returns, as high values of CX will reduce sensor gain.
`0074 The value of Cs also has an effect on sensitivity, and
`this can be increased in value with the trade-off of slower
`response time and more power. Increasing the electrode's
`surface area will not substantially increase touch sensitivity if
`its diameter is already significantly larger in Surface area than
`the object being detected. Panel material can also be changed
`to one having a higher dielectric constant, which will better
`help to propagate the field.
`0075 Ground planes around and under the electrode and
`its SNSK trace may lead to high CX loading and destroy gain.
`Thus in some cases the possible signal-to-noise ratio benefits
`of ground areas may be more than negated by the decreased
`gain from the circuit, and so ground areas around electrodes
`may be discouraged in Some circumstances. Metal areas near
`the electrode may reduce the field strength and increase CX
`loading and so it may be helpful if these are avoided if pos
`sible. It may be helpful to keep ground away from the elec
`trodes and traces.
`
`1.4 Recalibration Timeout
`0076 Ifan object or material obstructs the sense electrode
`the signal may rise enough to create a detection, preventing
`further operation. To help reduce the risk of this, the sensor
`includes a timer which monitors detections. If a detection
`exceeds the timer setting (known as the Max On-duration) the
`sensor performs a full recalibration. This does not toggle the
`output state but ensures that the QT 102 will detect a new
`touch correctly. The timer is set to activate this feature after
`~30 seconds. This will vary slightly with Cs.
`
`1.5 Forced Sensor Recalibration
`0077. The QT 102 has no recalibration pin; a forced reca
`libration is accomplished when the device is powered up,
`after the recalibration timeout or when the auto-off override is
`released.
`0078 However, supply drain is low so it is a simple matter
`to treat the entire IC as a controllable load; driving the
`QT102's VDD pin directly from another logic gate or a micro
`controller port will serve as both power and forced recal
`(ibration). The source resistance of most CMOS gates and
`microcontrollers are low enough to provide direct power
`without problems.
`1.6 Drift Compensation
`0079 Signal drift can occur because of changes in Cx and
`Cs over time. It may be helpful if drift is compensated for,
`otherwise false detections, nondetections, and sensitivity
`shifts may follow.
`0080 Drift compensation is schematically shown in FIG.
`2. Drift compensation is performed by making a reference
`level track the raw signal at a slow rate, but only while there
`is no detection in effect. It may be helpful if the rate of
`adjustment is performed relatively slowly, otherwise there
`
`may be a risk that legitimate detections may be ignored. The
`QT 102 drift compensates using a slew-rate limited change to
`the reference level; the threshold and hysteresis values are
`slaved to this reference.
`I0081. Once an object is sensed, the drift compensation
`mechanism ceases since the signal is legitimately high, and
`therefore should not cause the reference level to change (as
`indicated in FIG. 2 during the period between the vertical
`dotted lines).
`I0082. The QT 102’s drift compensation is asymmetric;
`the reference level drift-compensates in one direction faster
`than it does in the other. Specifically, it compensates faster for
`decreasing signals than for increasing signals. It may be help
`ful if increasing signals are not compensated for quickly,
`since an approaching finger could be compensated for par
`tially or entirely before approaching the sense electrode.
`I0083. However, an obstruction over the sense pad, for
`which the sensor has already made full allowance, could
`suddenly be removed leaving the sensor with an artificially
`elevated reference leveland thus become insensitive to touch.
`In this latter case, the sensor will compensate for the object's
`removal more quickly, for example in only a few seconds.
`I0084 With relatively large values of Cs and small values
`of Cx, drift compensation will appear to operate more slowly
`than with the converse. Note that the positive and negative
`drift compensation rates are different.
`1.7 Response Time
`I0085. The QT102’s response time is dependent on burst
`length, which in turn is dependent on Cs and Cx. With
`increasing Cs, response time slows, while increasing levels of
`Cx reduce response time.
`1.8 Spread Spectrum
`I0086. The QT102 modulates its internal oscillator by +7.5
`percent during the measurement burst. This spreads the gen
`erated noise over a wider band reducing emission levels. This
`also reduces Susceptibility since there is no longer a single
`fundamental burst frequency.
`2 Wiring and Parts
`I0087 FIG. 3 schematically shows a basic circuit configu
`ration for an implementation of an embodiment of the inven
`tion.
`
`2.1 Application Note
`I0088 Although not directly relevant for embodiments of
`the invention, for completeness, reference may be made to
`Application Note AN-KD02 (“Secrets of a Successful
`QTouchTM Design), included herein in its entirety by refer
`ence, and downloadable from the Quantum Research Group
`website, for information on example construction and design
`methods. Go to http://www.qprox.com, click the Support tab
`and then Application Notes.
`2.2 Cs Sample Capacitor
`I0089 Cs is the charge sensing sample capacitor. The
`required Cs value depends on the thickness of the panel and
`its dielectric constant. Thicker panels require larger values of
`Cs. Typical values are 1 or 2 nF to 50 nF depending on the
`sensitivity required; larger values of Cs may demand higher
`stability and better dielectric to ensure reliable sensing.
`
`Petitioner STMICROELECTRONICS, INC.,
`Ex. 1024, IPR2021-01161 Page 15 of 21
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`US 2009/0027068 A1
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`Jan. 29, 2009
`
`0090 The Cs capacitor may be a stable type, such as X7R
`ceramic or PPS film. For more consistent sensing from unit to
`unit, 5 percent tolerance capacitors are recommended. X7R
`ceramic types can be obtained in 5 percent tolerance for little
`or no extra cost. In applications where high sensitivity (long
`burst length) is required, the use of PPS capacitors is recom
`mended.
`
`2.3 RS Resistor
`0.091
`Series resistor Rs is in line with the electrode con
`nection and may be used to limit electrostatic discharge
`(ESD) currents and to suppress radio frequency interference
`(RFI). It may be approximately 4.7 kS2 to 33 kS2, for example.
`0092 Although this resistor may be omitted, the device
`may become susceptible to external noise or RFI. For more
`details of how to select these resistors see the Application
`Note AN-KDO2 referred to above in Section 2.1.
`
`2.4 Power Supply, PCB Layout
`0093. The power supply (between VDD and VSS/system
`